I usually add gelatin during the bottling process. I simply dissolve it with the priming sugar and pour it into the bottling bucket. Then, it's just a matter of racking the beer from the secondary (or primary) onto the solution.
I'm sure someone wiser than me will chime in, but I'd say you'd want to separate the sludge from the wort. I would just gently pour the liquid into another clean container.
Mine took awhile to start forming liquid. The sushi rice was really sticky, so that might've been part of the problem. Seems to be doing okay now though.